Field of the Invention
The present invention relates to transmission power reduction.
Related Art
3GPP (3rd Generation Partnership Project) LTE (long term evolution), an advanced version of UMTS (Universal Mobile Telecommunications System), is introduced in 3GPP release 8.
3GPP LTE adopts OFDMA (orthogonal frequency division multiple access) on downlink and SC-FDMA (Single Carrier-frequency division multiple access) on uplink. Knowledge of OFDM comes first for understanding OFDMA. OFDM may attenuate inter-slice boundary interference with low complexity and thus comes in use. OFDM converts data input in series into N parallel data items and transmits the converted data items on N orthogonal subcarriers. A subcarrier maintains frequency orthogonality. Meanwhile, OFDMA refers to a multiple access scheme that independently provides some of subcarriers available in a system adopting OFDM as its modulation scheme to each user, thus implementing multiple access.
FIG. 1 illustrates a 3GPP LTE wireless communication system.
As can be seen from FIG. 1, the wireless communication system includes at least one base station (BS) 20. Each base station 20 offers a communication service in a specific geographical area (generally denoted cell) 20a, 20b, and 20c. 
At this time, communication from the base station to a terminal is denoted downlink (DL), and communication from the terminal to the base station is denoted uplink (UL).
If a plurality of base stations by service providers are located at respective geographical regions 20a, 20b, and 20c, the base stations may interfere with each other.
In order to prevent the interference, the respective service providers may provide a service with different frequency bands.
However, when frequency bands of respective service operators are adjacent to each other, an interference problem still remains. The interference problem can be solved when transmission power is decreased or an actual frequency interval between adjacent bands is increased by limiting an amount of a transmission RB (resource block). However, when the transmission power is simply decreased or the transmission RB is limited, a service coverage is also decreased. Therefore, there is a need for a method of decreasing the transmission power to a proper level without causing an interference problem.